CVE-2026-82397
Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8.
| CWE | CWE-400 CWE-1284 |
| Vendor | tornadoweb |
| Product | tornado |
| Published | Aug 31, 2026 |
Get instant alerts for tornadoweb tornado
Be the first to know when new high vulnerabilities affecting tornadoweb tornado are published — delivered to Slack, Telegram or Discord.
CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H